In China mythology, what is the reason why Sanqingmen changed from Taoism to Buddhism after the war of deity?

In the novel Romance of Gods, Taoist immortals are still orthodox, while the western Tathagata is only a western immortal, and Guanyin is also a Taoist immortal. Buddhism, as evidenced by its history, was first introduced into the Han Dynasty. Today's Baima Temple in Luoyang is the earliest Buddhist temple. It should be the Eastern Han Dynasty. However, because local Taoism is mostly associated with divination and witchcraft, it has gradually lost its orthodox position. In addition, Taoism pays more attention to self-learning, so the concept of universal beings in Buddhism has the upper hand. Many original Taoist gods have been absorbed by Buddhism and become the protectors of Buddhism. Although Buddhism used to be a foreign religion, today's Buddhism is not the earliest Buddhism spread to the east. The birthplace of primitive Buddhism is almost extinct, and the homes of the four major schools of Buddhism are all in China.